This invention relates to automatic focusing devices for movie camera zoom lenses and more particularly to an efficient low power system for focusing same. In the past zoom lenses have been focused by movement of a heavy large diameter front objective. The weight of such objectives and their distance from the body of the camera has required that large and powerful motors be adapted to adjust them for automatic focus. Such focusing systems require heavy auxiliary batteries or quickly use regular batteries. It is an object of this invention to provide an automatic focus for a zoom lens system of a movie camera which does not require extra high capacity or large and heavy batteries to power the motor for the automatic focusing of the lens.